In response to the advent of the fifth generation of cellular mobile communications (5G communications) and in order to achieve the higher transmission data quantity, the frequency width of a modulation signal must be further increased from 20 MHz of LTE to a wider transmission bandwidth higher or equal to 100 MHz. In general, when the output power of the power amplifier increases, the degree of signal distortion becomes serious although the transmission efficiency is effectively increased. The power amplifier of the base transceiver station requires the very low degree of signal distortion, and usually uses the power back-off technology to achieve this target. However, the efficiency of the power amplifier is not good at this time.
Linearity can reflect the degree of signal distortion. If the linearity can be improved more effectively, then the greater output power and efficiency can be obtained. More particularly, in response to the advent of the 5G communications, the new technology for improving the broadband linearity further needs to be developed.